Electrical devices containing carbon nanotube-infused fibers and methods for production thereof

ABSTRACT

Electrical devices containing continuous fibers that are infused with carbon nanotubes are described herein. The electrical devices contain at least a first electrode layer and a second electrode layer, where the first and second electrode layers each contain a plurality of continuous fibers that are infused with carbon nanotubes. In some embodiments, the electrical devices can be supercapacitors, further containing at least a base plate, a layer of separator material disposed between the first and second electrode layers, and an electrolyte in contact with the first and second electrode layers. The first and second electrode layers can be formed by conformal winding of the continuous fibers. The electrical devices can contain any number of additional electrode layers, each being separated from one another by a layer of separator material. Methods for producing the electrical devices are also described herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119from U.S. Provisional Patent Application Ser. No. 61/309,827, filed Mar.2, 2010, which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention generally relates to energy storage, and, morespecifically, energy storage using carbon nanotubes.

BACKGROUND

Capacitors are electrical devices that are used to accumulate and storeelectric charge. Capacitors are distinguished from batteries in at leasttwo aspects. First, storage of electric charge in a capacitor is basedupon physical charge separation rather than the chemical separation of abattery. Second, charge and discharge rates of a capacitor are much morerapid than the chemical reactions that occur in a battery.

In conventional capacitors, charge separation is maintained by twoconductive plates that are separated by a dielectric material. In thepresence of an applied potential, an electric field builds in thedielectric material and produces a mechanical force between theconductive plates. The ratio of the electric charge maintained on theconductive plates to the potential difference between them is referredto as the capacitance, which is measured in Farads.

Various modifications of conventional capacitors have also beendeveloped. Electrolytic capacitors utilize an ion-containing liquid asone of its conductive plates. Such electrolytic capacitors typicallydisplay much higher capacitance values than do conventional capacitors.However, their utility is somewhat limited by a requirement that eachconductive plate is to be maintained in a polarized voltage state.

Supercapacitors, also known as electric double-layer capacitors,electrochemical double-layer capacitors, supercondensors,ultracapacitors, or pseudocapacitors, can display even highercapacitance values. Supercapacitors differ significantly fromconventional capacitors and electrolytic capacitors in that there is nota significant physical separation of the conductive plates in asupercapacitor. Instead, supercapacitors maintain charge separation byincorporating a vanishingly thin physical barrier between the conductiveplates (<100 μm). The physical barrier effectively maintains chargeseparation when the supercapacitor is in the charged state, while beingsufficiently permeable to charge carriers to allow rapid charge anddischarge rates.

Many conventional supercapacitors presently use activated carbonparticles as a high surface area substrate to hold charge carriers froman electrolyte dispersed therein. Although activated carbon particleshave a high surface area, certain charge carriers are too large topenetrate the porous interior of the activated carbon particles and takeadvantage of its high surface area. FIG. 1 shows a schematic of anillustrative prior art supercapacitor 100 containing activated carbonparticles 105. Supercapacitor 100 contains conductive layers 101 and102, connected to positive terminal 103 and negative terminal 104,respectively. Conductive layers 101 and 102 each contain activatedcarbon particles 105 and an electrolyte containing positive ions 106 andnegative ions 107 admixed with activated carbon particles 105. Positiveions 106 and negative ions 107 can reside about the interior or exteriorof activated carbon particles 105. Conductive layers 101 and 102 arephysically isolated from one another by a layer of separator material108, which is permeable to positive ions 106 and negative ions 107 ofthe electrolyte. As shown in FIG. 1, supercapacitor 100 is in adischarged state.

Certain high performance materials, including carbon nanotubes, havebeen proposed as a replacement for activated carbon particles insupercapacitors due their high accessible surface area. Carbon nanotubescan be further advantageous in this regard due to their electricalconductivity. Although carbon nanotubes have significant potential forimproving the performance of supercapacitors, research efforts to datehave only been successful in randomly dispersing small quantities ofcarbon nanotubes in the electrolyte medium of a supercapacitor. As such,current fabrication techniques are only amenable to production of smallcarbon nanotube-containing supercapacitors with low electrical storagecapabilities.

In view of the foregoing, high-volume supercapacitors and otherelectrical devices containing large quantities of carbon nanotubes wouldbe of significant benefit in the art. It would also be of considerablebenefit to provide methods for readily preparing such high-volumesupercapacitors having enhanced electrical storage capabilities. Thepresent invention satisfies these needs and provides related advantagesas well.

SUMMARY

In some embodiments, electrical devices described herein include a firstelectrode layer and a second electrode layer, where the first electrodelayer and the second electrode layer contain a plurality of continuousfibers that are infused with carbon nanotubes.

In some embodiments, methods described herein include providing aplurality of continuous fibers that are infused with carbon nanotubes,forming a first electrode layer from a first portion of the plurality ofcontinuous fibers, and forming a second electrode layer from a secondportion of the plurality of continuous fibers.

In other embodiments, methods described herein include providing aplurality of continuous fibers that are infused with carbon nanotubes,forming a first electrode layer by winding a portion of the plurality ofcontinuous fibers conformally about a base plate, and forming at leasttwo additional electrode layers over the first electrode layer bywinding separate portions of the plurality of continuous fibersconformally over the first electrode layer.

The foregoing has outlined rather broadly the features of the presentdisclosure in order that the detailed description that follows can bebetter understood. Additional features and advantages of the disclosurewill be described hereinafter, which form the subject of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionsto be taken in conjunction with the accompanying drawings describing aspecific embodiments of the disclosure, wherein:

FIG. 1 shows a schematic of an illustrative prior art supercapacitorcontaining activated carbon particles;

FIG. 2A shows an isometric schematic of the first electrode layer in anillustrative embodiment of the present supercapacitors; FIG. 2B shows anisometric schematic of the first electrode layer in an illustrativeembodiment of the present supercapacitors in which an electrode terminalis located on the base plate;

FIG. 3 shows a schematic of an illustrative embodiment of the presentsupercapacitors as viewed parallel to the longitudinal axes of thecontinuous fibers of the electrode layers;

FIG. 4 shows a schematic of a coin press sample supercapacitorstructure; and

FIG. 5 shows an illustrative cyclic voltammogram of a supercapacitor ofthe present disclosure.

DETAILED DESCRIPTION

The present disclosure is directed, in part, to electrical devicescontaining electrode layers formed from continuous fibers that have beeninfused with carbon nanotubes. Such continuous fibers are also referredto herein as carbon nanotube-infused fibers or carbon nanotube-infusedfiber materials. The present disclosure is also directed, in part, tomethods for making electrical devices having electrode layers formedfrom continuous fibers that have been infused with carbon nanotubes.

As previously set forth, supercapacitors typically display much highercapacitance values than do conventional capacitors or electrolyticcapacitors. Accordingly, they have garnered significant interest inenergy storage applications such as solar energy collection,hydroelectric energy collection, and wind farm energy collection. Therapid charge and discharge cycles of supercapacitors make them wellsuited for these purposes and others, since the supercapacitors canreadily take on excess energy when electrical grid demand is low andquickly release their stored energy when electrical grid demand is high.Further, supercapacitors are capable of being non-degradably charged anddischarged many hundreds of thousands of times, making them considerablysuperior to batteries in this regard. In addition, the rapid charge anddischarge cycles of supercapacitors and their charge/discharge stabilitymake them particularly useful for applications in which multiple cyclesof rapid charging and discharging are desirable such as, for example, inhybrid gas-electric vehicles.

With growing interest in the above applications and others,supercapacitors that have even higher energy storage limits than thosecurrently available are needed. The capacitance in supercapacitors isproportional to the electrode surface area (e.g., the area of theconductive plates). In conventional supercapacitors containing activatedcarbon particles, there is an intrinsic limit as to how much theeffective electrode surface area can be increased. That is, theactivated carbon particles used in conventional supercapacitors can onlybe made so small before an asymptotic capacitance value is reached.Further, limited pore sizes in the activated carbon particles reducetheir effective surface area and can be problematic for someelectrolytes. Because carbon nanotubes provide a much higher effectivesurface area per unit weight than does activated carbon, these entitiesoffer the potential to significantly increase the capacitance ofsupercapacitors. Despite their promise in supercapacitor applications,it has heretofore been difficult to place carbon nanotubes intosupercapacitors in a state that can take advantage of their exceedinglyhigh effective surface area.

Embodiments of the present disclosure describe electrical devicescontaining electrodes made from continuous fibers that have been infusedwith carbon nanotubes. Such continuous carbon nanotube-infused fibersare described in commonly assigned, co-pending U.S. patent applicationSer. Nos. 12/611,073, 12/611,101, and 12/611,103, all filed on Nov. 2,2009, and 12/938,328, filed on Nov. 2, 2010, each of which isincorporated herein by reference in its entirety. The fiber material ofsuch carbon nanotube-infused fibers can generally vary withoutlimitation and can include, for example, glass fibers, carbon fibers,metal fibers, ceramic fibers, and organic fibers (e.g., aramid fibers)for example. Such carbon nanotube-infused fibers can be readily preparedin spoolable lengths from commercially available continuous fibers orcontinuous fiber forms (e.g., fiber tows or fiber tapes). In addition,the carbon nanotubes' lengths, diameter, and coverage density canreadily be varied by the above-referenced methods.

Depending on their growth conditions, the carbon nanotubes of the carbonnanotube-infused fibers can also be oriented such that they aresubstantially perpendicular to the surface of the fiber material or suchthat they are substantially parallel to the longitudinal axis of thefiber material. In the present embodiments, by using carbonnanotube-infused fibers having substantially perpendicular carbonnanotubes, a better exposure of an electrolyte to the carbon nanotubesurface area can be realized. This is particularly true, when the carbonnanotubes are present in a substantially unbundled state. Theabove-referenced methods for preparing carbon nanotube-infused fibersare particularly adept at achieving a substantially perpendicularorientation and a substantially unbundled state, thereby providingcarbon nanotube-infused fibers having a high effective surface area foruse in the present embodiments. Additional details concerning the carbonnanotube-infused fibers and methods for production thereof are set forthhereinafter.

Not only can carbon nanotubes replace activated carbon particles insupercapacitor embodiments of the present electrical devices, but thecarbon nanotube-infused fibers become indistinct from the electrodeitself in such cases. In conventional supercapacitors containingactivated carbon particles, there are electrode plates that are incontact with the activated carbon particles (see FIG. 1). In the presentsupercapacitor embodiments, the carbon nanotube-infused fibers are notin contact with a separate electrode plate, thereby making theelectrodes the carbon nanotube-infused fibers themselves. This featurerepresents a new paradigm in supercapacitor design. In addition, thedesign of the present supercapacitor embodiments allows multipleelectrode layers to be incorporated therein, thereby further increasingthe amount of electrical energy that can be stored. Depending on thesize of the continuous fibers and the length, diameter, and coveragedensity of carbon nanotubes thereon, effective electrode surface areascan be realized that are up to about 14,000 times that of conventionalsupercapacitors containing activated carbon particles. As previouslynoted, all of these parameters can be readily varied in the preparationof carbon nanotube-infused fibers and can be used to tune the presentsupercapacitor embodiments to a desired capacitance.

As used herein, the terms “fiber,” “fiber material,” or “filament”equivalently refer to any material that has a fibrous component as abasic structural feature. As used herein, the term “continuous fibers”refers to spoolable lengths of fiber materials such as individualfilaments, yarns, rovings, tows, tapes, ribbons, woven and non-wovenfabrics, plies, mats, and the like.

As used herein, the terms “spoolable lengths” or “spoolable dimensions”equivalently refer to a fiber material that has at least one dimensionthat is not limited in length, thereby allowing the fiber material to bestored on a spool or mandrel following infusion with carbon nanotubes. Afiber material of “spoolable lengths” or “spoolable dimensions” has atleast one dimension that indicates the use of either batch or continuousprocessing for carbon nanotube infusion thereon.

As used herein, the term “infused” refers to being bonded and “infusion”refers to the process of bonding. As used herein, the terms “carbonnanotube-infused fiber” or “carbon nanotube-infused fiber material”equivalently refer to a fiber material that has carbon nanotubes bondedthereto. Such bonding of carbon nanotubes to a fiber material caninvolve mechanical attachment, covalent bonding, ionic bonding, pi-piinteractions (pi-stacking interactions), and/or van der Waalsforce-mediated physisorption. In some embodiments, the carbon nanotubescan be directly bonded to the fiber material. In other embodiments, thecarbon nanotubes can be indirectly bonded to the fiber material via abarrier coating and/or catalytic nanoparticles used to mediate growth ofthe carbon nanotubes. The particular manner in which the carbonnanotubes are infused to the fiber material can be referred to as thebonding motif.

As used herein, the term “nanoparticle” refers to particles having adiameter between about 0.1 nm and about 100 nm in equivalent sphericaldiameter, although nanoparticles need not necessarily be spherical inshape. As used herein, the term “catalytic nanoparticle” refers to ananoparticle that possesses catalytic activity for mediating carbonnanotube growth.

As used herein, the term “transition metal” refers to any element oralloy of elements in the d-block of the periodic table (Groups 3 through12), and the term “transition metal salt” refers to any transition metalcompound such as, for example, transition metal oxides, carbides,nitrides, and the like. Illustrative transition metals that formcatalytic nanoparticles suitable for synthesizing carbon nanotubesinclude, for example, Ni, Fe, Co, Mo, Cu, Pt, Au, Ag, alloys thereof,salts thereof, and mixtures thereof.

As used herein, the terms “sizing agent,” or “sizing,” collectivelyrefer to materials used in the manufacture of fiber materials as acoating to protect the integrity of the fiber material, to provideenhanced interfacial interactions between the fiber material and amatrix material, and/or to alter and/or to enhance certain physicalproperties of the fiber material.

As used herein, the term “uniform in length” refers to a condition inwhich carbon nanotubes have lengths with tolerances of plus or minusabout 20% or less of the total carbon nanotube length, for carbonnanotube lengths ranging from about 1 μm to about 500 μm. At very shortcarbon nanotube lengths (e.g., about 1 μm to about 4 μm), the tolerancecan be plus or minus about 1 μm, that is, somewhat more than about 20%of the total carbon nanotube length.

As used herein, the term “uniform in density distribution” refers to acondition in which the carbon nanotube coverage density on a fibermaterial has a tolerance of plus or minus about 10% over the fibermaterial surface area that is covered with carbon nanotubes.

As used herein, the term “continuous process” refers to a multi-stageprocess that operates in a substantially uninterrupted manner,particularly a process for producing carbon nanotube-infused fibers.

In some embodiments, electrical devices described herein include a firstelectrode layer and a second electrode layer, where the first electrodelayer and the second electrode layer contain a plurality of continuousfibers that are infused with carbon nanotubes. In some embodiments, theelectrical devices are supercapacitors.

In some embodiments, the electrical devices further include a baseplate, an electrolyte in contact with the first electrode layer and thesecond electrode layer, and a layer of separator material disposedbetween the first electrode layer and the second electrode layer, wherethe separator material is permeable to ions of the electrolyte. In someembodiments, the plurality of continuous fibers of the first electrodelayer are conformally wound about the base plate, and the plurality ofcontinuous fibers of the second electrode layer are conformally woundabout the layer of separator material.

The types of carbon nanotubes infused to the continuous fibers cangenerally vary without limitation. In various embodiments, the carbonnanotubes infused to the continuous fibers can be, for example, any of anumber of cylindrically-shaped carbon allotropes of the fullerene familyincluding single-wall carbon nanotubes, double-wall carbon nanotubes,multi-wall carbon nanotubes, and any combination thereof. In someembodiments, the carbon nanotubes can be capped with a fullerene-likestructure. Stated another way, the carbon nanotubes have closed ends insuch embodiments. However, in other embodiments, the carbon nanotubescan remain open-ended. In some embodiments, closed carbon nanotube endscan be opened through treatment with an appropriate oxidizing agent(e.g., HNO₃/H₂SO₄). In some embodiments, the carbon nanotubes canencapsulate other materials. In some embodiments, the carbon nanotubescan be covalently functionalized after becoming infused to the fibermaterial. In some embodiments, a plasma process can be used to promotefunctionalization of the carbon nanotubes.

Carbon nanotubes can be metallic, semimetallic or semiconductingdepending on their chirality. An established system of nomenclature fordesignating a carbon nanotube's chirality is recognized by those ofordinary skill in the art and is distinguished by a double index (n,m),where n and m are integers that describe the cut and wrapping ofhexagonal graphite when formed into a tubular structure. In addition tochirality, a carbon nanotube's diameter also influences its electricalconductivity and the related property of thermal conductivity. In thesynthesis of carbon nanotubes, the carbon nanotubes' diameters can becontrolled by using catalytic nanoparticles of a given size. Typically,a carbon nanotube's diameter is approximately that of the catalyticnanoparticle that catalyzes its formation. Therefore, carbon nanotubes'properties can be controlled in one respect by adjusting the size of thecatalytic nanoparticles used in their synthesis, for example. By way ofnon-limiting example, catalytic nanoparticles having a diameter of about1 nm can be used to infuse a fiber material with single-wall carbonnanotubes. Larger catalytic nanoparticles can be used to preparepredominantly multi-wall carbon nanotubes, which have larger diametersbecause of their multiple nanotube layers, or mixtures of single-walland multi-wall carbon nanotubes. Multi-wall carbon nanotubes typicallyhave a more complex conductivity profile than do single-wall carbonnanotubes due to interwall reactions that can occur between theindividual nanotube layers and redistribute current non-uniformly. Bycontrast, there is no change in current across different portions of asingle-wall carbon nanotube.

In general, the carbon nanotubes infused to the continuous fibers can beof any length. Longer carbon nanotubes are generally more advantageousin the present supercapacitor embodiments, since they can provideelectrodes having a higher effective surface area. In variousembodiments, the carbon nanotubes can have a length ranging betweenabout 1 μm and about 1000 μm or between about 1 μm and about 500 μm. Insome embodiments, the carbon nanotubes can have a length ranging betweenabout 100 μm and about 500 μm. In other embodiments, the carbonnanotubes can have a length ranging between about 1 μm and about 50 μmor between about 10 μm and about 25 μm. In some embodiments, the carbonnanotubes can be substantially uniform in length.

In some embodiments, an average length of the carbon nanotubes rangesbetween about 1 μm and about 500 μm, including about 1 μm, about 2 μm,about 3 μm, about 4 μm, about 5 about 6 μm, about 7 μm, about 8 μm,about 9 μm, about 10 μm, about 15 μm, about 20 μm, about 25 μm, about 30μm, about 35 μm, about 40 μm, about 45 μm, about 50 μm, about 60 μm,about 70 μm, about 80 μm, about 90 μm, about 100 μm, about 150 μm, about200 μm, about 250 μm, about 300 μm, about 350 μm, about 400 μm, about450 μm, about 500 μm, and all values and subranges therebetween. In someembodiments, an average length of the carbon nanotubes is less thanabout 1 μm, including about 0.5 μm, for example, and all values andsubranges therebetween. In some embodiments, an average length of thecarbon nanotubes ranges between about 1 μm and about 10 including, forexample, about 1 μm, about 2 μm, about 3 μm, about 4 μm, about 5 μm,about 6 μm, about 7 μm, about 8 μm, about 9 μm, about 10 μm, and allvalues and subranges therebetween. In still other embodiments, anaverage length of the carbon nanotubes is greater than about 500 μm,including, for example, about 510 μm, about 520 μm, about 550 μm, about600 μm, about 700 μm, and all values and subranges therebetween.

The average length of the carbon nanotubes can be one factor thatdetermines the weight percentage of carbon nanotubes infused to thecontinuous fiber. In general, the carbon nanotube-infused fibersdescribed in the above-referenced, co-pending patent applications havemuch higher carbon nanotube loading percentages than can be obtained byother methods. For example, carbon nanotube-infused fibers can containbetween about 1% to about 30% or even about 40% to about 50% infusedcarbon nanotubes by weight. The chosen carbon nanotube weight percentagecan be dictated by the desired capacitance in the present supercapacitorembodiments.

The carbon nanotube coverage density on the continuous fibers can beanother factor that determines the weight percentage of infused carbonnanotubes. In some embodiments, the carbon nanotubes infused to thefiber material are generally uniform in density distribution, referringto the uniformity of the carbon nanotube density that is infused to thefiber material. As defined above, the tolerance for a uniform densitydistribution is plus or minus about 10% over the fiber material surfacearea that is infused with carbon nanotubes. By way of non-limitingexample, this tolerance is equivalent to about ±1500 carbonnanotubes/μm² for a carbon nanotube having a diameter of 8 nm and 5walls. Such a figure assumes that the space inside the carbon nanotubeis fillable. In some embodiments, the maximum carbon nanotube density,expressed as a percent coverage of the fiber material (i.e., thepercentage of the fiber material surface area that is covered withcarbon nanotubes) can be as high as about 55%, again assuming a carbonnanotube having an 8 nm diameter, 5 walls and fillable space within. 55%surface area coverage is equivalent to about 15,000 carbon nanotubes/μm²for a carbon nanotube having the referenced dimensions. In someembodiments, the density of coverage is up to about 15,000 carbonnanotubes/μm². One of ordinary skill in the art will recognize that awide range of carbon nanotube density distributions can be attained byvarying the disposition of the catalytic nanoparticles on the surface ofthe fiber material, the exposure time of the fiber material to carbonnanotube growth conditions, and the actual growth conditions themselvesused to infuse the carbon nanotubes to the fiber material.

In some embodiments, the density of carbon nanotube coverage on thecontinuous fibers can be adjusted to account for a change in the size ofthe ions of an electrolyte. For example, if an electrolyte containslarger ions, a lower density of carbon nanotube coverage on thecontinuous fibers can be used to ensure satisfactory ion mobility andelectrode contact during charge and discharge cycles of varioussupercapacitor embodiments.

In accordance with some of the present embodiments, a plurality ofcontinuous fibers that are infused with carbon nanotubes form theelectrode layers of a supercapacitor. The first electrode layer can beformed by winding the continuous fibers about a central base plate, andthe second electrode layer and any additional electrode layers can beformed by winding the continuous fibers over the first electrode layer.A layer of separator material is disposed between the electrode layers.FIG. 2A shows an isometric schematic of the first electrode layer in anillustrative embodiment of the present supercapacitors. As shown in FIG.2, continuous fiber 201 is conformally wound about base plate 200 toform the first electrode layer of the present supercapacitors. Terminalend 202 of continuous fiber 201 can be attached to an electrode terminalfor charging or discharging the supercapacitor. The electrode terminalcan be located on the base plate in some embodiments or placed elsewherein other embodiments. FIG. 2B shows an isometric schematic of the firstelectrode layer in an illustrative embodiment of the presentsupercapacitors in which electrode terminal 204 is located on base plate200. Continuous fiber 201 is conformally wound about base plate 200, andterminal end 202 of continuous fiber 201 is attached to electrodeterminal 204. Electrode terminal 204 can optionally be electricallyisolated from base plate 200 via insulator material 205, if desired. Asecond electrode terminal can also be included on base plate 200 forconnection to the continuous fibers of other electrode layers, ifdesired (not shown).

Although FIGS. 2A and 2B have shown spacing between adjacent windings ofcontinuous fiber 201, it is to be understood that the spacing depictedis for purposes of illustration clarity only. As will be evident to oneof ordinary skill in the art, by having adjacent windings of continuousfiber 201 as closely spaced as possible, a larger number of carbonnanotubes per unit area can be obtained, thereby leading to higherelectrode layer surface areas and a higher capacitance per unit weightof continuous fiber. It should be noted, however, that the spacingbetween adjacent windings of continuous fiber 201 can be varied, ifneeded, to provide a desired capacitance in a supercapacitor of a givensize.

Although not precluded in the present embodiments, it is generally truethat there is substantially no overlap between adjacent windings ofcontinuous fiber 201, as this would produce electrode layers having asmaller surface area per unit weight of continuous fiber. Accordingly,in some embodiments, the continuous fibers of the electrode layers aresubstantially parallel to one another in order to avoid such overlap.However, some overlap of continuous fiber 201 in adjacent windings canbe used to adjust the capacitance, if desired, as described previouslyfor embodiments where there is spacing between adjacent windings. Itshould be noted that some contact between individual continuous fibersin higher order continuous fiber structures (e.g., fiber tows, fiberribbons and/or fiber tapes) can be tolerated as long as the electrolytehas sufficient access to the surface area of the individual continuousfibers.

After formation of the first electrode layer as described above, a layerof separator material that is permeable to ions of an electrolyte canthen be disposed on the first electrode layer. Subsequently, a secondelectrode layer can be formed on the layer of separator material bywinding a separate portion of continuous fibers about the layer ofseparator material. Deposition of additional layers of separatormaterial and winding of continuous fibers thereon can be conducted, ifdesired, to form a supercapacitor having more than two electrode layers.

FIG. 3 shows a schematic of an illustrative embodiment of the presentsupercapacitors as viewed parallel to the longitudinal axes of thecontinuous fibers of the electrode layers. Supercapacitor 300 of FIG. 3contains two electrode layers, although more electrode layers can beadded as described above. As shown in FIG. 3, supercapacitor 300contains base plate 301 about which is wrapped continuous fiber 302 (seeFIGS. 2A and 2B) having carbon nanotubes 303 infused thereon. Sectionsof continuous fiber 302 looping between the top and bottom of base plate301 have been omitted for clarity. A layer of separator material 304 isdisposed upon continuous fiber 302 and carbon nanotubes 303. Continuousfiber 305 having carbon nanotubes 306 infused thereon are wrapped aboutthe layer of separator material 304. Again, sections of continuous fiber305 looping between the top and bottom of the layer of separator 304have been omitted for clarity. An electrolyte (not shown) is associatedwith continuous fibers 302 and 305 and carbon nanotubes 303 and 306infused thereon. The layer of separator material 304 provides chargeseparation between the first electrode layer and the second electrodelayer.

Referring still to FIG. 3, supercapacitor 300 can further include outerinsulator casing 307 to contain the electrolyte therein and to provideelectrical isolation. Illustrative outer insulating casings can include,for example, an insulating box containing supercapacitor 300 or aninsulating shrink wrap covering supercapacitor 300. The nature of theouter insulator casing 307 can be varied according to the desiredoperational needs of the supercapacitor. For example, if it desired thatsupercapacitor 300 remains flexible or if release of the electrolyte isnot a concern, a simple plastic shrink wrap outer insulator casing canbe sufficient to contain the components therein. However, ifsupercapacitor 300 needs more mechanical support or if release of theelectrolyte is a particular concern, outer insulator casing 307 can bemade from a more rigid material (e.g., a plastic box).

In some embodiments, outer insulator casing 307 can be omitted. Forexample, by placing supercapacitor 300 (without outer insulator casing307) in a reservoir of electrolyte, a working supercapacitor can beproduced. In this case, there is an excess of electrolyte about theoutermost electrode layer, which for the supercapacitor of FIG. 3 is thesecond electrode layer (continuous fibers 305 and carbon nanotubes 306infused thereon). The excess of electrolyte about the second electrodelayer does not significantly alter the operational principles of thesupercapacitor. In these embodiments, the container for the electrolytereservoir can be considered to be the outer insulator casing 307 ofsupercapacitor 300. For example, the electrolyte reservoir can becontained in a plastic bucket or like container. However, it is notrequired that the container for the electrolyte reservoir be aninsulator in these embodiments, as the container can be electricallyisolated from its environment in other ways, if desired.

In general, continuous fibers of any type that can infused with carbonnanotubes can be used in the present supercapacitors and methods forproduction thereof. As described above, continuous fibers such as, forexample, glass fibers, carbon fibers, metal fibers, ceramic fibers, andorganic fibers can be successfully infused with carbon nanotubes.Additional details concerning the carbon nanotube-infused fibers andmethods for their production are set forth hereinbelow.

In various embodiments, individual continuous fibers (i.e., individualfilaments) have a diameter ranging between about 1 μm and about 100 μm.Continuous length fibers having diameters in this range are readilyavailable from a variety of commercial sources.

In some embodiments, the carbon nanotubes infused to the continuousfibers are substantially perpendicular to the surface of the continuousfibers. Although carbon nanotube-infused fibers can be produced suchthat they have the infused carbon nanotubes present in any desiredorientation, one of ordinary skill in the art will recognize that asubstantially perpendicular orientation will maximize the carbonnanotube surface area and, hence, the electrode layer surface area. Forat least this reason, a substantially perpendicular orientation of thecarbon nanotubes is advantageous in the present embodiments.

In some embodiments, the continuous fibers can be electricallyconductive before being infused with carbon nanotubes. Illustrativeconductive fibers that can be used in the present embodiments include,for example, carbon fibers and metal fibers (e.g., stainless steel,aluminum, copper and the like). Although carbon nanotube infusion to thecontinuous fibers imparts electrical conductivity thereto, bettercurrent collection and charge storage properties are generally observedwhen the continuous fibers are initially electrically conductive beforecarbon nanotube infusion. In alternative embodiments, however, thecontinuous fibers can be non-conductive before being infused with carbonnanotubes. In such embodiments, a conductivity enhancer can be used inassociation with the continuous fibers in order to enhance currentcollection and charge storage. For example, a metal form such as metalfoils, metal ribbons, metal powders, and/or metal nanoparticles can beincluded with the continuous fibers in the present embodiments. In suchembodiments, the metal nanoparticles can include residual catalyticnanoparticles used for mediating carbon nanotube growth. Suchconductivity enhancers can also be used when the continuous fibers areconductive as well. In some embodiments, the present electrical devicesfurther contain a conductivity enhancer associated with the firstelectrode layer and the second electrode layer, where the conductivityenhancer includes at least one metal form such as, for example, metalfoils, metal ribbons, metal powders, metal nanoparticles, and the like.

In general, the continuous fibers are used in a higher order fiber formin the present embodiments, rather than being placed therein asindividual filaments. Such higher order fiber forms vary widely instructure and are considered in further detail immediately hereinafter.In some embodiments, the fiber form of the continuous fibers can be, forexample, a fiber tow, a fiber tape, and/or a fiber ribbon. In otherembodiments, the fiber form can be, for example, a fiber roving, a yarn,a fiber braid, a woven or non-woven fabric, a fiber ply, and/or a fibermat. In some embodiments, the individual filaments are substantiallyparallel to one another in the higher order fiber form. In someembodiments, the continuous fibers are substantially parallel to oneanother in the first electrode layer and the second electrode layer. Insome embodiments, there is substantially no overlap of the continuousfibers in adjacent windings about the base plate and the layer(s) ofseparator material when used in supercapacitors.

Rovings include soft strands of continuous fiber that have been twisted,attenuated and freed of foreign matter.

Fiber tows are generally compactly associated bundles of continuousfibers, which can be twisted together to give yarns in some embodiments.Yarns include closely associated bundles of twisted fibers, wherein eachfiber diameter in the yarn is relatively uniform. Yarns have varyingweights described by their ‘tex,’ (expressed as weight in grams per 1000linear meters), or ‘denier’ (expressed as weight in pounds per 10,000yards). For yarns, a typical tex range is usually between about 200 andabout 2000.

Fiber braids are rope-like structures of densely packed continuousfibers. Such rope-like structures can be assembled from yarns, forexample. Braided structures can optionally include a hollow portion.Alternately, a braided structure can be assembled about another corematerial.

Fiber tows can also include associated bundles of untwisted continuousfibers. Thus, fiber tows are a convenient form for manipulating largequantities of substantially parallel fibers in a single operation. As inyarns, the individual fiber diameters in a fiber tow are generallyuniform. Fiber tows also have varying weights and a tex range that isusually between about 200 and 2000. In addition, fiber tows arefrequently characterized by the number of thousands of individual fibersin the fiber tow, such as, for example, a 12K tow, a 24K tow, a 48K tow,and the like.

Tapes and ribbons contain continuous fibers that can be assembled asweaves or as non-woven flattened fiber tows, for example. Tapes can varyin width and are generally two-sided structures similar to a ribbon. Asdescribed in Applicants' co-pending patent applications, carbonnanotubes can be infused to a tape on one or both sides of the tape.Further, carbon nanotubes of different types, diameters or lengths canbe grown on each side of a tape.

In some embodiments, the continuous fibers can be organized into fabricor sheet-like structures. These include, for example, woven fabrics,non-woven fabrics, non-woven fiber mats and fiber plies, in addition tothe tapes described above. Such higher ordered structures can beassembled from parent continuous fibers, fiber tows, yarns, or the like.

The identity of base plate of the present supercapacitor embodiments isnot particularly limited. In some embodiments, the base plate is aninsulator material (e.g., a non-conductive material). In suchembodiments, the role of the base plate is primarily structural andprovides a support for building the present supercapacitors thereon.Such non-conductive base plates can vary over a wide composition rangeand include, for example, plastics, ceramics, aluminum oxide, siliconoxide, and wood. The rigidity and mechanical strength of the base platecan be adjusted for a given application. For example, it can bedesirable for the base plate to be flexible in some embodiments, suchthat supercapacitor itself maintains some degree of flexibility.Likewise, if the supercapacitor is intended for an application in whichpayload weight is a concern, for example, a lightweight base plate canbe used (e.g., a foamed polyurethane or polystyrene). In alternativeembodiments, the base plate can be an electrical conductor, if desired.In embodiments in which the base plate is electrically conductive, itcan particularly augment the current collection properties of the firstelectrode layer.

The dimensions of the base plate are not particularly limited, exceptthat the base plate should be capable of mechanically supporting thesupercapacitor and its components. Ultimately, the size of the baseplate determines the surface area of the electrode layers after havingcontinuous fibers wound thereon, which produces higher capacitancevalues. Depending on the desired capacitance and any operational sizerestrictions for the resulting supercapacitor, the base plate can have asurface area ranging from about 1 cm² to about 100,000 cm². In someembodiments, the base plate is thin (e.g., a pseudo-two dimensionalstructure), such that at least the majority of its surface area isdetermined by the combined area of its top and bottom faces. Forexample, the base plate can have a thickness such that greater thanabout 95% of its surface area resides on its top and bottom faces. Inother embodiments, the base plate can be a true three dimensional solidsuch that less than about 95% of its surface area resides on its top andbottom faces. Illustrative shapes of the base plate can include, forexample, cylinders, spheres, hemispheres, triangular prisms, rectangularprisms, square prisms, rhombic prisms, trapezoidal prisms, pentagonalprisms, hexagonal prisms, heptagonal prisms, octagonal prisms, nonagonalprisms, decagonal prisms, and the like. Although the supercapacitorsexemplified by FIGS. 2A, 2B and 3 have been shown with a rectangularprism base plate, it is to be understood that any of the aforementionedbase plate shapes can be utilized while still operating within thespirit and scope of the present disclosure.

In some embodiments, the present electrical devices can further includean outer insulator casing. Illustrative insulator casings include, forexample, plastics and wax. In some embodiments, the outer insulatorcasing can be a shrink wrap material (e.g., a plastic shrink wrap). Ingeneral, any dielectric material can be used to provide electricalisolation for the electrical devices and to contain the variouscomponents therein. When there are two electrode layers, the outerinsulator casing can be disposed about the second electrode layer. Whenthere are additional electrode layers, the outer insulator casing casebe disposed about the outermost electrode layer. In supercapacitorembodiments where an outer insulator casing is present, a first portionof the electrolyte resides between the base plate and the layer ofseparator material, and a second portion of the electrolyte residesbetween the layer of separator material and the outer insulator casing.As noted previously, the outer insulator casing can optionally beomitted such as, for example, when the supercapacitor is placed in areservoir of electrolyte that contacts the electrode layers in somemanner. That is, in such supercapacitor embodiments, the base plate, thefirst electrode layer, the second electrode layer, and the layer ofseparator material reside in a reservoir of the electrolyte.

In some embodiments, the outer insulator casing has a thickness rangingbetween about 100 μm and about 10 cm. In other embodiments, the outerinsulator casing has a thickness ranging between about 5 mm and about 5cm or between about 1 cm and about 4 cm. In still other embodiments, theouter insulator casing has a thickness ranging between 10 μm and about 1mm or between about 100 μm and about 1 mm. In general, the outerinsulator casing is made as thin as possible to provide electricalisolation of the electrical device while still maintaining structuralintegrity thereof. As one of ordinary skill in the art will recognize,thin outer insulator casings keep material costs lower and allow lowerweight supercapacitors and other electrical devices to be produced.

As previously described, the present electrical devices can furtherinclude electrode terminals to which the continuous fibers of at leastthe first electrode layer and the second electrode layer are connected.In some embodiments, the present electrical devices further include afirst electrode terminal connected to the plurality of continuous fibersof the first electrode layer and a second electrode terminal connectedto the continuous fibers of the second electrode layer. In embodimentswhere additional electrode layers are present, a corresponding number ofadditional electrode terminals can be included as well. When present,the electrode terminals can be located on the base plate in someembodiments. In embodiments where the base plate is electricallyconductive, the electrode terminals can be electrically isolated fromthe base plate by an insulator material. In alternative embodiments, theelectrode terminals can be located off the base plate. For example, theelectrode terminals can be located on the outer insulator casing, ifdesired. In still other embodiments, the continuous fibers of the firstelectrode layer, the second electrode layer, and additional electrodelayers, if present, can be connected directly to an electrical powersource and/or electrical load without being connected thereto throughintervening electrode terminals.

The layer of separator material in the present supercapacitorembodiments can be formed from any material of sufficient thickness thatis capable of maintaining charge separation of the ions of theelectrolyte once the supercapacitor is in a charged state. In general,the separator material is a thin film dielectric substance that isporous in nature and allows for high ion mobility between the electrodelayers when the supercapacitor is charging or discharging but is capableof maintaining charge separation once the supercapacitor reaches acharged state. Thus, the layer of separator material is selectivelypermeable to movement of charge carriers across it. In some embodiments,the separator material can be a non-woven polymer fabric such as, forexample, polyethylene non-woven fabrics, polypropylene non-wovenfabrics, polyester non-woven fabrics, and polyacrylonitrile non-wovenfabrics. In other embodiments, the separator material can be a poroussubstance such as, for example, a porous poly(vinylidenefluoride)-hexafluoropropane copolymer film, a porous cellulose film,kraft paper, rayon woven fabrics, and the like. Generally, any separatormaterial that can be used in batteries can also be used in the presentsupercapacitors.

The degree of porosity of the separator material is such that the ionsof the electrolyte are sufficiently mobile so as to move across theseparator material when the supercapacitor is being charged ordischarged but sufficiently immobile so as to maintain charge separationonce the supercapacitor reaches a charged state. In some embodiments,the porosity of the separator material is greater than about 90%. Insome embodiments, the porosity of the separator material ranges betweenabout 90% and about 95%. In other embodiments, the porosity of theseparator material ranges between about 90% and about 40%, or betweenabout 87% and about 50%, or between about 85% and about 65%.

In addition to porosity, the thickness of the separator material cangovern the degree of ion mobility across the separator material. For agiven porosity, a thicker layer of separator material provides greatercharge separation and lower ion mobility than does a thinner layer ofseparator material. In some embodiments, the thickness of the layer ofseparator material is less than about 100 μm. In some embodiments, thethickness of the layer of separator material ranges between about 100 μmand about 50 μm. In some embodiments, the thickness of the layer ofseparator material ranges between about 50 μm and about 25 μm or betweenabout 25 μm and about 10 μm. In some embodiments, the thickness of thelayer of separator material is less than about 10 μm. In someembodiments, the thickness of the layer of separator material rangesbetween about 10 μm and about 1 μm. In some embodiments, the thicknessof the layer of separator material is less than about 1 μm. In someembodiments, the thickness of the layer of separator material rangesbetween about 100 nm and about 1 μm. In some embodiments, a thickness ofthe layer of separator material can be optimized to achieve a balancebetween electrolyte volume and voltage standoff capability.

In one embodiment, a suitable separator material can be a high porosity(e.g., >90%) polypropylene and/or polyethylene electrolytic membrane.Such electrolytic membranes are available from Celgard LLC of Charlotte,N.C. These electrolytic membranes exhibit a high electric voltagestandoff capability, thereby permitting a thinner and lighter film forisolating the electrode layers. In some embodiments, a paper separatormaterial (e.g., kraft paper) can also be used.

The electrolyte of the present supercapacitor embodiments is notparticularly limited. In some embodiments, the electrolyte can be aninorganic electrolyte. In other embodiments, the electrolyte can be anorganic electrolyte. As one of ordinary skill in the art will recognize,aqueous electrolytes offer low internal resistance values but have aworking range limited to about 1 V. In contrast, organic electrolyteshave a working voltage range of up to about 2.5 V or about 3 V but havea higher internal resistance. As with other components of the presentsupercapacitor embodiments, the electrolyte identity and concentrationcan be altered to account for different end uses

Illustrative aqueous electrolytes include aqueous acid solutions (e.g.,sulfuric acid, phosphoric acid, hydrochloric acid, and the like),aqueous base solutions (e.g., sodium hydroxide or potassium hydroxide),and neutral solutions. Neutral electrolyte solutions are generallyformed by dissolving a salt in an aqueous medium. Illustrative saltsthat are suitable for use as neutral electrolytes include, for example,sodium chloride, potassium chloride, sodium oxide, potassium oxide,sodium sulfate, potassium sulfate, and the like. Additional aqueouselectrolytes can be envisioned by those of ordinary skill in the art. Ingeneral, the concentration of the aqueous electrolyte ranges betweenabout 0.1 and 20 M or between about 1 wt. % and 100 wt. %.

Organic electrolytes include an electrolytic species dissolved in anorganic solvent. Illustrative electrolytic species include, for example,tetraalkylammonium salts (e.g., tetraethylammonium ortetramethylammonium halides and hydroxides); quaternary phosphoniumsalts; and lithium, sodium or potassium tetrafluoroborates,perchlorates, hexafluorophosphates, bis(trifluoromethane)sulfonates,bis(trifluoromethane)sulfonylimides, ortris(trifluoromethane)sulfonylmethides. In general, the concentration ofthe electrolytic species in the organic solvent ranges between about 0.1M and about 5 M or between about 0.5 M and about 3 M.

Organic solvents used in organic electrolytes are generally aproticorganic solvents having a high dielectric constant. Illustrative organicsolvents that can be used in an organic electrolyte include, withoutlimitation, alkyl carbonates (e.g., propylene carbonate, ethylenecarbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate,dipropyl carbonate, methyl ethyl carbonate, methyl butyl carbonate,methyl propyl carbonate, ethyl propyl carbonate, butyl propyl carbonate,1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate,and 2,3-pentene carbonate), nitriles (e.g., acetonitrile, acrylonitrile,propionitrile, butyronitrile and benzonitrile), sulfoxides (e.g.,dimethyl sulfoxide, diethyl sulfoxide, ethyl methyl sulfoxide, andbenzylmethyl sulfoxide), amides (e.g., formamide, methylformamide, anddimethylformamide), pyrrolidones (e.g., N-methylpyrrolidone), lactones(e.g., γ-butyrolactone, γ-valerolactone, 2-methyl-γ-butyrolactone, andacetyl-γ-butyrolactone), phosphate triesters, nitromethane, ethers(e.g., 1,2-dimethoxyethane; 1,2-diethoxyethane; 1,2-methoxyethoxyethane;1,2- or 1,3-dimethoxypropane; 1,2- or 1,3-diethoxypropane; 1,2- or1,3-ethoxymethoxypropane; 1,2-dibutoxyethane; tetrahydrofuran;2-methyltetrahydrofuran and other alkyl, dialkyl, alkoxy or dialkoxytetrahydrofurans; 1,4-dioxane; 1,3-dioxolane; 1,4-dioxolane;2-methyl-1,3-dioxolane; 4-methyl-1,3-dioxolane; sulfolane;3-methylsulfolane; methyl ether; ethyl ether; propyl ether; diethyleneglycol dialkyl ether; triethylene glycol dialkyl ethers; ethylene glycoldialkyl ethers; and tetraethylene glycol dialkyl ethers), esters (e.g.,alkyl propionates such as methyl or ethyl propionate, dialkyl malonatessuch as diethyl malonate, alkyl acetates such as methyl acetate andethyl acetate, and alkyl formates such as methyl formate and ethylformate); and maleic anhydride. In addition, organic gels and the likecan be used, if desired.

In some embodiments, the electrolyte can be an ionic liquid such as, forexample, benzyldimethylpropylammonium aluminum tetrachlorate,benzyldimethylammonium imide, ethylmethylammonium bisulfate,1-butyl-3-methylimidazolium tetrafluoroborate, or tetraethylammoniumtetrafluoroborate. Any of the above organic solvents can optionally beused in combination with such ionic liquids.

In various embodiments, the present electrical devices can contain morethan two electrode layers. In some embodiments, the electrical devicesfurther contain at least one additional layer of separator material andat least one additional electrode layer containing a plurality ofcontinuous fibers that are infused with carbon nanotubes. In suchembodiments, each electrode layer is separated from one another by alayer of separator material. Further, the electrolyte is in contact witheach electrode layer in such embodiments. By repeating the electrode andseparator material layering, a supercapacitor having any number ofdesired layers can be formed. For example, a supercapacitor weighingtens to hundreds of pounds and having a capacitance of several thousandFarads can be obtained by repeating the electrode layering.

Capacitance values of the present supercapacitor embodiments can varyover a wide range. In various embodiments, the supercapacitors of thepresent disclosure can have a capacitance ranging between about 0.5Farad/gram of continuous fibers and about 500 Farad/gram of continuousfibers. In some embodiments, the supercapacitors have a capacitanceranging between about 1 Farad/gram of continuous fibers and about 250Farad/gram of continuous fibers. In still other embodiments, thesupercapacitors have a capacitance ranging between about 2 Farad/gram ofcontinuous fibers and about 100 Farad/gram of continuous fibers. In someembodiments, the supercapacitors have a capacitance of at least about 1Farad/gram of continuous fibers. In other embodiments, thesupercapacitors have a capacitance of at least about 2 Farad/gram ofcontinuous fibers. It should be noted that the foregoing values are forsupercapacitors having only two electrode layers. When thesupercapacitors have more than two electrode layers, the capacitanceincreases in substantially direct proportion to the number of additionalelectrode layers. That is, a supercapacitor having three electrodelayers has about twice the capacitance of a supercapacitor having onlytwo electrode layers. In addition, the supercapacitors can be usedsingly or stacked in series.

FIG. 4 shows a schematic of a coin press sample supercapacitorstructure. Such a supercapacitor structure can be readily prepared fortesting of the supercapacitors described herein by connecting outerportion 400 and inner portion 401 to form supercapacitor 402. FIG. 5shows an illustrative cyclic voltammogram of a supercapacitor of thepresent disclosure.

In some embodiments, methods described herein include providing aplurality of continuous fibers that are infused with carbon nanotubes,forming a first electrode layer from a first portion of the plurality ofcontinuous fibers, and forming a second electrode layer from a secondportion of the plurality of continuous fibers.

In some embodiments, the methods further include exposing the firstelectrode layer and the second electrode layer to an electrolyte, andapplying a layer of separator material between the first electrode layerand the second electrode layer, where the separator material ispermeable to ions of the electrolyte. In some embodiments, forming afirst electrode layer involves winding the first portion of theplurality of continuous fibers conformally about a base plate, andforming a second electrode layer involves winding the second portion ofthe plurality of continuous fibers conformally over the first electrodelayer. In some embodiments, winding to form the first electrode layer,winding to form the second electrode layer, and applying the layer ofseparator material can all occur simultaneously. In other embodiments,each layer can be wound or applied separately.

In some embodiments, the methods further include applying at least oneadditional layer of separator material over the second electrode layerand winding at least one additional electrode layer over the secondelectrode layer. In such embodiments, the at least one additionalelectrode layer contains a plurality of continuous fibers that areinfused with carbon nanotubes, and each electrode layer is separatedfrom one another by a layer of separator material. Further, theelectrolyte is in contact with each electrode layer.

In other embodiments, methods described herein include providing aplurality of continuous fibers that are infused with carbon nanotubes,forming a first electrode layer by winding a portion of the plurality ofcontinuous fibers conformally about a base plate, and forming at leasttwo additional electrode layers over the first electrode layer bywinding separate portions of the plurality of continuous fibersconformally over the first electrode layer.

In some embodiments, the methods further include exposing the firstelectrode layer and the at least two additional electrode layers to anelectrolyte, and applying a layer of separator material between eachelectrode layer, where the separator material is permeable to ions ofthe electrolyte.

In some embodiments, the plurality of continuous fibers are in a fiberform such as, for example, a fiber tow, a fiber tape, and/or a fiberribbon. In some embodiments, the plurality of continuous fibers aresubstantially parallel to one another in the electrode layers. In someembodiments, the individual filaments of the plurality of continuousfibers are substantially parallel to one another in the fiber form. Infurther embodiments, there is substantially no overlap of the pluralityof continuous fibers in adjacent windings of the electrode layers. Inaddition, when there are additional electrode layers, there can also besubstantially no overlap in those layers as well. Optionally, there canbe spacing between adjacent windings, if desired.

In some embodiments, the first electrode layer is exposed to theelectrolyte before applying the layer of separator material. However,since the layer of separator material is permeable to the ions of theelectrolyte, the first electrode layer can also be exposed to theelectrolyte at a later stage of fabrication in alternative embodiments.In some embodiments, the first electrode layer, the second electrodelayer, and additional electrode layers, if present, can besimultaneously exposed to the electrolyte. In some embodiments, thefirst electrode layer, the second electrode layer, and additionalelectrode layers, if present, can be simultaneously exposed to theelectrolyte by simultaneous immersion in a reservoir of the electrolyte.

In some embodiments, the methods further include applying an outerinsulator casing to the electrode layers. Additional details concerningthe outer insulator casing have been set forth hereinabove.

Embodiments disclosed herein utilize carbon nanotube-infused fibers thatcan be readily prepared by methods described in commonly-owned,co-pending U.S. patent application Ser. Nos. 12/611,073, 12/611,101,12/611,103, and 12/938,328 each of which is incorporated by referenceherein in its entirety. A brief description of the processes describedtherein follows.

To infuse carbon nanotubes to a fiber material, the carbon nanotubes aresynthesized directly on the fiber material. In some embodiments, this isaccomplished by first disposing a carbon nanotube-forming catalyst(e.g., catalytic nanoparticles) on the fiber material. A number ofpreparatory processes can be performed prior to this catalystdeposition.

In some embodiments, the fiber material can be optionally treated with aplasma to prepare the fiber surface to accept the catalyst. For example,a plasma treated glass fiber material can provide a roughened glassfiber surface in which the carbon nanotube-forming catalyst can bedeposited. In some embodiments, the plasma also serves to “clean” thefiber surface. The plasma process for “roughing” the fiber surface thusfacilitates catalyst deposition. The roughness is typically on the scaleof nanometers. In the plasma treatment process craters or depressionsare formed that are nanometers deep and nanometers in diameter. Suchsurface modification can be achieved using a plasma of any one or moreof a variety of different gases, including, without limitation, argon,helium, oxygen, ammonia, nitrogen and hydrogen.

In some embodiments, where a fiber material being employed has a sizingmaterial associated with it, such sizing can be optionally removed priorto catalyst deposition. Optionally, the sizing material can be removedafter catalyst deposition. In some embodiments, sizing material removalcan be accomplished during carbon nanotube synthesis or just prior tocarbon nanotube synthesis in a pre-heat step. In other embodiments, somesizing materials can remain throughout the entire carbon nanotubesynthesis process.

Yet another optional step prior to or concomitant with deposition of thecarbon nanotube-forming catalyst (i.e., catalytic nanoparticles) isapplication of a barrier coating on the fiber material. Barrier coatingsare materials designed to protect the integrity of sensitive fibermaterials, such as carbon fibers, organic fibers, glass fibers, metalfibers, and the like. Such a barrier coating can include, for example,an alkoxysilane, an alumoxane, alumina nanoparticles, spin on glass andglass nanoparticles. For example, in an embodiment the barrier coatingis Accuglass T-11 Spin-On Glass (Honeywell International Inc.,Morristown, N.J.). The carbon nanotube-forming catalyst can be added tothe uncured barrier coating material and then applied to the fibermaterial together, in one embodiment. In other embodiments, the barriercoating material can be added to the fiber material prior to depositionof the carbon nanotube-forming catalyst. In such embodiments, thebarrier coating can be partially cured prior to catalyst deposition. Thebarrier coating material can be of a sufficiently thin thickness toallow exposure of the carbon nanotube-forming catalyst to the carbonfeedstock gas for subsequent CVD—or like carbon nanotube growth. In someembodiments, the barrier coating thickness is less than or about equalto the effective diameter of the carbon nanotube-forming catalyst. Oncethe carbon nanotube-forming catalyst and the barrier coating are inplace, the barrier coating can be fully cured. In some embodiments, thethickness of the barrier coating can be greater than the effectivediameter of the carbon nanotube-forming catalyst so long as it stillpermits access of carbon nanotube feedstock gases to the sites of thecatalyst. Such barrier coatings can be sufficiently porous to allowaccess of carbon feedstock gases to the carbon nanotube-formingcatalyst.

In some embodiments, the thickness of the barrier coating ranges betweenabout 10 nm and about 100 nm. In other embodiments, the thickness of thebarrier coating ranges between about 10 nm and about 50 nm, including 40nm. In some embodiments, the thickness of the barrier coating is lessthan about 10 nm, including about 1 nm, about 2 nm, about 3 nm, about 4nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, andabout 10 nm, including all values and subranges therebetween.

Without being bound by theory, the barrier coating can serve as anintermediate layer between the fiber material and the carbon nanotubesand mechanically infuses the carbon nanotubes to the fiber material.Such mechanical infusion via a barrier coating provides a robust systemfor carbon nanotube growth in which the fiber material serves as aplatform for organizing the carbon nanotubes, while still allowing thebeneficial carbon nanotube properties to be conveyed to the fibermaterial. Moreover, benefits of including a barrier coating include, forexample, protection of the fiber material from chemical damage due tomoisture exposure and/or thermal damage at the elevated temperaturesused to promote carbon nanotube growth.

As described further below, the carbon nanotube-forming catalyst can beprepared as a liquid solution that contains the carbon nanotube-formingcatalyst as transition metal catalytic nanoparticles. The diameters ofthe synthesized carbon nanotubes are related to the size of thetransition metal catalytic nanoparticles as described above.

Carbon nanotube synthesis can be based on a chemical vapor deposition(CVD) process or related carbon nanotube growth process which occurs atelevated temperatures. In some embodiments, the CVD-based growth processcan be plasma-enhanced by providing an electric field during the growthprocess such that the carbon nanotube growth follows the direction ofthe electric field. Other illustrative carbon nanotube growth processesinclude, for example, micro-cavity, laser ablation, flame synthesis, arcdischarge, and high pressure carbon monoxide (HiPCO) synthesis. Thespecific temperature is a function of catalyst choice, but can typicallybe in a range of about 500° C. to about 1000° C. Accordingly, carbonnanotube synthesis involves heating the fiber material to a temperaturein the aforementioned range to support carbon nanotube growth.

In some embodiments, CVD-promoted carbon nanotube growth on thecatalyst-laden fiber material is performed. The CVD process can bepromoted by, for example, a carbon-containing feedstock gas such asacetylene, ethylene, and/or ethanol. The carbon nanotube growthprocesses also generally use an inert gas (e.g., nitrogen, argon, and/orhelium) as a primary carrier gas. The carbon-containing feedstock gas istypically provided in a range from between about 0% to about 15% of thetotal mixture. A substantially inert environment for CVD growth can, beprepared by removal of moisture and oxygen from the growth chamber.

In the carbon nanotube growth process, carbon nanotubes grow at thesites of transition metal catalytic nanoparticles that are operable forcarbon nanotube growth. The presence of a strong plasma-creatingelectric field can be optionally employed to affect carbon nanotubegrowth. That is, the growth tends to follow the direction of theelectric field. By properly adjusting the geometry of the plasma sprayand electric field, vertically aligned carbon nanotubes (i.e.,perpendicular to the surface of the fiber material) can be synthesized.Under certain conditions, even in the absence of a plasma,closely-spaced carbon nanotubes can maintain a substantially verticalgrowth direction resulting in a dense array of carbon nanotubesresembling a carpet or forest.

Returning to the catalyst deposition process, a carbon nanotube-formingcatalyst is deposited to provide a layer (typically no more than amonolayer) of catalytic nanoparticles on the fiber material for thepurpose of growing carbon nanotubes thereon. The operation of depositingcatalytic nanoparticles on the fiber material can be accomplished by anumber of techniques including, for example, spraying or dip coating asolution of catalytic nanoparticles or by gas phase deposition, whichcan occur by a plasma process. Thus, in some embodiments, after forminga catalyst solution in a solvent, the catalyst can be applied byspraying or dip coating the fiber material with the solution, orcombinations of spraying and dip coating. Either technique, used aloneor in combination, can be employed once, twice, thrice, four times, upto any number of times to provide a fiber material that is sufficientlyuniformly coated with catalytic nanoparticles that are operable forformation of carbon nanotubes. When dip coating is employed, forexample, a fiber material can be placed in a first dip bath for a firstresidence time in the first dip bath. When employing a second dip bath,the fiber material can be placed in the second dip bath for a secondresidence time. For example, fiber materials can be subjected to asolution of carbon nanotube-forming catalyst for between about 3 secondsto about 90 seconds depending on the dip configuration and linespeed.Employing spraying or dip coating processes, a fiber material with acatalyst surface density of less than about 5% surface coverage to ashigh as about 80% surface coverage can be obtained. At higher surfacedensities (e.g., about 80%), the carbon nanotube-forming catalystnanoparticles are nearly a monolayer. In some embodiments, the processof coating the carbon nanotube-forming catalyst on the fiber materialproduces no more than a monolayer. For example, carbon nanotube growthon a stack of carbon nanotube-forming catalyst can erode the degree ofinfusion of the carbon nanotubes to the fiber material. In otherembodiments, transition metal catalytic nanoparticles can be depositedon the fiber material using evaporation techniques, electrolyticdeposition techniques, and other processes known to those of ordinaryskill in the art, such as addition of the transition metal catalyst to aplasma feedstock gas as a metal organic, metal salt or other compositionpromoting gas phase transport.

Because processes to manufacture carbon nanotube-infused fibers aredesigned to be continuous, a spoolable fiber material can be dip-coatedin a series of baths where dip coating baths are spatially separated. Ina continuous process in which nascent fibers are being generated denovo, such as newly formed glass fibers from a furnace, dip bath orspraying of a carbon nanotube-forming catalyst can be the first stepafter sufficiently cooling the newly formed fiber material. In someembodiments, cooling of newly formed glass fibers can be accomplishedwith a cooling jet of water which has the carbon nanotube-formingcatalyst particles dispersed therein.

In some embodiments, application of a carbon nanotube-forming catalystcan be performed in lieu of application of a sizing when generating afiber and infusing it with carbon nanotubes in a continuous process. Inother embodiments, the carbon nanotube-forming catalyst can be appliedto newly formed fiber materials in the presence of other sizing agents.Such simultaneous application of a carbon nanotube-forming catalyst andother sizing agents can provide the carbon nanotube-forming catalyst insurface contact with the fiber material to insure carbon nanotubeinfusion. In yet further embodiments, the carbon nanotube-formingcatalyst can be applied to nascent fibers by spray or dip coating whilethe fiber material is in a sufficiently softened state, for example,near or below the annealing temperature, such that the carbonnanotube-forming catalyst is slightly embedded in the surface of thefiber material. When depositing the carbon nanotube-forming catalyst onhot glass fiber materials, for example, care should be given to notexceed the melting point of the carbon nanotube-forming catalyst,thereby causing nanoparticle fusion and loss of control of the carbonnanotube characteristics (e.g., diameter) as a result.

Carbon nanotubes infused to a fiber material can serve to protect thefiber material from conditions including, for example, moisture,oxidation, abrasion, compression and/or other environmental conditions.In this case, the carbon nanotubes themselves can act as a sizing agent.Such a carbon nanotube-based sizing agent can be applied to a fibermaterial in lieu of or in addition to conventional sizing agents. Whenpresent, conventional sizing agents can be applied before or after theinfusion and growth of carbon nanotubes on the fiber material.Conventional sizing agents vary widely in type and function and include,for example, surfactants, anti-static agents, lubricants, siloxanes,alkoxysilanes, aminosilanes, silanes, silanols, polyvinyl alcohol,starch, and mixtures thereof. Such conventional sizing agents can beused to protect the carbon nanotubes themselves from various conditionsor to convey further properties to the fiber material that are notimparted by the carbon nanotubes. In some embodiments, a conventionalsizing agent can be removed from the fiber material prior to carbonnanotube growth. Optionally, a conventional sizing agent can be replacedwith another conventional sizing agent that is more compatible with thecarbon nanotubes or the carbon nanotube growth conditions.

The carbon nanotube-forming catalyst solution can be a transition metalnanoparticle solution of any d-block transition metal. In addition, thenanoparticles can include alloys and non-alloy mixtures of d-blockmetals in elemental form, in salt form, and mixtures thereof. Such saltforms include, without limitation, oxides, carbides, and nitrides,acetates, nitrates, and the like. Non-limiting illustrative transitionmetal nanoparticles include, for example, Ni, Fe, Co, Mo, Cu, Pt, Au,and Ag, salts thereof and mixtures thereof. Many transition metalnanoparticle catalysts are readily commercially available from a varietyof suppliers, including, for example, Ferrotec Corporation (Bedford,N.H.).

Catalyst solutions used for applying the carbon nanotube-formingcatalyst to the fiber material can be in any common solvent that allowsthe carbon nanotube-forming catalyst to be uniformly dispersedthroughout. Such solvents can include, without limitation, water,acetone, hexane, isopropyl alcohol, toluene, ethanol, methanol,tetrahydrofuran (THF), cyclohexane or any other solvent with controlledpolarity to create an appropriate dispersion of the carbonnanotube-forming catalytic nanoparticles therein. Concentrations ofcarbon nanotube-forming catalyst in the catalyst solution can be in arange from about 1:1 to about 1:10,000 catalyst to solvent.

In some embodiments, after applying the carbon nanotube-forming catalystto the fiber material, the fiber material can be optionally heated to asoftening temperature. This step can aid in embedding the carbonnanotube-forming catalyst in the surface of the fiber material toencourage seeded growth and prevent tip growth where the catalyst floatsat the tip of the leading edge a growing carbon nanotube. In someembodiments heating of the fiber material after disposing the carbonnanotube-forming catalyst on the fiber material can be at a temperaturebetween about 500° C. and about 1000° C. Heating to such temperatures,which can be used for carbon nanotube growth, can serve to remove anypre-existing sizing agents on the fiber material allowing deposition ofthe carbon nanotube-forming catalyst directly on the fiber material. Insome embodiments, the carbon nanotube-forming catalyst can also beplaced on the surface of a sizing coating prior to heating. The heatingstep can be used to remove sizing material while leaving the carbonnanotube-forming catalyst disposed on the surface of the fiber material.Heating at these temperatures can be performed prior to or substantiallysimultaneously with introduction of a carbon-containing feedstock gasfor carbon nanotube growth.

In some embodiments, the process of infusing carbon nanotubes to a fibermaterial includes removing sizing agents from the fiber material,applying a carbon nanotube-forming catalyst to the fiber material aftersizing removal, heating the fiber material to at least about 500° C.,and synthesizing carbon nanotubes on the fiber material. In someembodiments, operations of the carbon nanotube infusion process includeremoving sizing from a fiber material, applying a carbonnanotube-forming catalyst to the fiber material, heating the fibermaterial to a temperature operable for carbon nanotube synthesis andspraying a carbon plasma onto the catalyst-laden fiber material. Thus,where commercial fiber materials are employed, processes forconstructing carbon nanotube-infused fibers can include a discrete stepof removing sizing from the fiber material before disposing thecatalytic nanoparticles on the fiber material. Some commercial sizingmaterials, if present, can prevent surface contact of the carbonnanotube-forming catalyst with the fiber material and inhibit carbonnanotube infusion to the fiber material. In some embodiments, wheresizing removal is assured under carbon nanotube growth conditions,sizing removal can be performed after deposition of the carbonnanotube-forming catalyst but just prior to or during providing acarbon-containing feedstock gas.

The step of synthesizing carbon nanotubes can include numeroustechniques for forming carbon nanotubes, including, without limitation,micro-cavity, thermal or plasma-enhanced CVD techniques, laser ablation,arc discharge, flame synthesis, and high pressure carbon monoxide(HiPCO). During CVD, in particular, a sized fiber material with carbonnanotube-forming catalyst disposed thereon, can be used directly. Insome embodiments, any conventional sizing agents can be removed duringcarbon nanotube synthesis. In some embodiments other sizing agents arenot removed, but do not hinder carbon nanotube synthesis and infusion tothe fiber material due to the diffusion of the carbon-containingfeedstock gas through the sizing. In some embodiments, acetylene gas canbe ionized to create a jet of cold carbon plasma for carbon nanotubesynthesis. The plasma is directed toward the catalyst-laden fibermaterial. Thus, in some embodiments synthesizing carbon nanotubes on afiber material includes (a) forming a carbon plasma; and (b) directingthe carbon plasma onto the catalyst disposed on the fiber material. Thediameters of the carbon nanotubes that are grown are dictated by thesize of the carbon nanotube-forming catalyst. In some embodiments, asized fiber material can be heated to between about 550° C. and about800° C. to facilitate carbon nanotube growth. To initiate the growth ofcarbon nanotubes, two or more gases are bled into the reactor: an inertcarrier gas (e.g., argon, helium, or nitrogen) and a carbon-containingfeedstock gas (e.g., acetylene, ethylene, ethanol or methane). Carbonnanotubes grow at the sites of the carbon nanotube-forming catalyst.

In some embodiments, a CVD growth process can be plasma-enhanced. Aplasma can be generated by providing an electric field during the growthprocess. Carbon nanotubes grown under these conditions can follow thedirection of the electric field. Thus, by adjusting the geometry of thereactor, vertically aligned carbon nanotubes can be grown where thecarbon nanotubes are substantially perpendicular to the surface of thefiber material (i.e., radial growth). In some embodiments, a plasma isnot required for radial growth to occur about the fiber material. Forfiber materials that have distinct sides such as, for example, tapes,mats, fabrics, plies, and the like, the carbon nanotube-forming catalystcan be disposed on one or both sides of the fiber material.Correspondingly, under such conditions, carbon nanotubes can be grown onone or both sides of the fiber material as well.

As described above, the carbon nanotube synthesis is performed at a ratesufficient to provide a continuous process for infusing spoolable lengthfiber materials with carbon nanotubes. Numerous apparatus configurationsfacilitate such a continuous synthesis as exemplified below.

In some embodiments, carbon nanotube-infused fiber materials can beprepared in an “all-plasma” process. In such embodiments, the fibermaterials pass through numerous plasma-mediated steps to form the finalcarbon nanotube-infused fiber materials. The first of the plasmaprocesses, can include a step of fiber surface modification. This is aplasma process for “roughing” the surface of the fiber material tofacilitate catalyst deposition, as described above. As also describedabove, surface modification can be achieved using a plasma of any one ormore of a variety of different gases, including, without limitation,argon, helium, oxygen, ammonia, hydrogen, and nitrogen.

After surface modification, the fiber material proceeds to catalystapplication. In the present all-plasma process, this step is a plasmaprocess for depositing the carbon nanotube-forming catalyst on the fibermaterial. The carbon nanotube-forming catalyst is typically a transitionmetal as described above. The transition metal catalyst can be added toa plasma feedstock gas as a precursor in non-limiting forms including,for example, a ferrofluid, a metal organic, a metal salt, mixturesthereof or any other composition suitable for promoting gas phasetransport. The carbon nanotube-forming catalyst can be applied at roomtemperature in ambient environment with neither vacuum nor an inertatmosphere being required. In some embodiments, the fiber material canbe cooled prior to catalyst application.

Continuing the all-plasma process, carbon nanotube synthesis occurs in acarbon nanotube-growth reactor. Carbon nanotube growth can be achievedthrough the use of plasma-enhanced chemical vapor deposition, whereincarbon plasma is sprayed onto the catalyst-laden fibers. Since carbonnanotube growth occurs at elevated temperatures (typically in a range ofabout 500° C. to about 1000° C. depending on the catalyst), thecatalyst-laden fibers can be heated prior to being exposed to the carbonplasma. For the carbon nanotube infusion process, the fiber material canbe optionally heated until softening occurs. After heating, the fibermaterial is ready to receive the carbon plasma. The carbon plasma can begenerated, for example, by passing a carbon-containing feedstock gassuch as, for example, acetylene, ethylene, ethanol, and the like,through an electric field that is capable of ionizing the gas. This coldcarbon plasma is directed, via spray nozzles, to the fiber material. Thefiber material can be in close proximity to the spray nozzles, such aswithin about 1 centimeter of the spray nozzles, to receive the plasma.In some embodiments, heaters can be disposed above the fiber material atthe plasma sprayers to maintain the elevated temperature of the fibermaterial.

Another configuration for continuous carbon nanotube synthesis involvesa special rectangular reactor for the synthesis and growth of carbonnanotubes directly on fiber materials. The reactor can be designed foruse in a continuous in-line process for producing carbonnanotube-infused fiber materials. In some embodiments, carbon nanotubesare grown via a CVD process at atmospheric pressure and an elevatedtemperature in the range of about 550° C. and about 800° C. in amulti-zone reactor. The fact that the carbon nanotube synthesis occursat atmospheric pressure is one factor that facilitates the incorporationof the reactor into a continuous processing line for carbon nanotubeinfusion to the fiber materials. Another advantage consistent within-line continuous processing using such a zone reactor is that carbonnanotube growth occurs in seconds, as opposed to minutes (or longer), asin other procedures and apparatus configurations typical in the art.

Carbon nanotube synthesis reactors in accordance with the variousembodiments include the following features:

Rectangular Configured Synthesis Reactors: The cross-section of atypical carbon nanotube synthesis reactor known in the art is circular.There are a number of reasons for this including, for example,historical reasons (e.g., cylindrical reactors are often used inlaboratories) and convenience (e.g., flow dynamics are easy to model incylindrical reactors, heater systems readily accept circular tubes(e.g., quartz, etc.), and ease of manufacturing. Departing from thecylindrical convention, the present disclosure provides a carbonnanotube synthesis reactor having a rectangular cross section. Thereasons for the departure include at least the following:

1) Inefficient Use of Reactor Volume. Since many fiber materials thatcan be processed by the reactor are relatively planar (e.g., flat tapes,sheet-like forms, or spread tows or rovings), a circular cross-sectionis an inefficient use of the reactor volume. This inefficiency resultsin several drawbacks for cylindrical carbon nanotube synthesis reactorsincluding, for example, a) maintaining a sufficient system purge;increased reactor volume requires increased gas flow rates to maintainthe same level of gas purge, resulting in inefficiencies for high volumeproduction of carbon nanotubes in an open environment; b) increasedcarbon-containing feedstock gas flow rates; the relative increase ininert gas flow for system purge, as per a) above, requires increasedcarbon-containing feedstock gas flow rates. Consider that the volume ofan illustrative 12K glass fiber roving is about 2000 times less than thetotal volume of a synthesis reactor having a rectangular cross-section.In an equivalent cylindrical reactor (i.e., a cylindrical reactor thathas a width that accommodates the same planarized glass fiber materialas the rectangular cross-section reactor), the volume of the glass fibermaterial is about 17,500 times less than the volume of the reactor.Although gas deposition processes, such as CVD, are typically governedby pressure and temperature alone, volume can have a significant impacton the efficiency of deposition. With a rectangular reactor there is astill excess volume, and this excess volume facilitates unwantedreactions. However, a cylindrical reactor has about eight times thatvolume available for facilitating unwanted reactions. Due to thisgreater opportunity for competing reactions to occur, the desiredreactions effectively occur more slowly in a cylindrical reactor. Such aslow down in carbon nanotube growth, is problematic for the developmentof continuous growth processes. Another benefit of a rectangular reactorconfiguration is that the reactor volume can be decreased further stillby using a small height for the rectangular chamber to make the volumeratio better and the reactions even more efficient. In some embodimentsdisclosed herein, the total volume of a rectangular synthesis reactor isno more than about 3000 times greater than the total volume of a fibermaterial being passed through the synthesis reactor. In some furtherembodiments, the total volume of the rectangular synthesis reactor is nomore than about 4000 times greater than the total volume of the fibermaterial being passed through the synthesis reactor. In some stillfurther embodiments, the total volume of the rectangular synthesisreactor is less than about 10,000 times greater than the total volume ofthe fiber material being passed through the synthesis reactor.Additionally, it is notable that when using a cylindrical reactor, morecarbon-containing feedstock gas is required to provide the same flowpercent as compared to reactors having a rectangular cross section. Itshould be appreciated that in some other embodiments, the synthesisreactor has a cross-section that is described by polygonal forms thatare not rectangular, but are relatively similar thereto and provide asimilar reduction in reactor volume relative to a reactor having acircular cross section; and c) problematic temperature distribution;when a relatively small-diameter reactor is used, the temperaturegradient from the center of the chamber to the walls thereof is minimal,but with increased reactor size, such as would be used forcommercial-scale production, such temperature gradients increase.Temperature gradients result in product quality variations across thefiber material (i.e., product quality varies as a function of radialposition). This problem is substantially avoided when using a reactorhaving a rectangular cross-section. In particular, when a planarsubstrate is used, reactor height can be maintained constant as the sizeof the substrate scales upward. Temperature gradients between the topand bottom of the reactor are essentially negligible and, as aconsequence, thermal issues and the product-quality variations thatresult are avoided.

2) Gas introduction. Because tubular furnaces are normally employed inthe art, typical carbon nanotube synthesis reactors introduce gas at oneend and draw it through the reactor to the other end. In someembodiments disclosed herein, gas can be introduced at the center of thereactor or within a target growth zone, symmetrically, either throughthe sides or through the top and bottom plates of the reactor. Thisimproves the overall carbon nanotube growth rate because the incomingfeedstock gas is continuously replenishing at the hottest portion of thesystem, which is where carbon nanotube growth is most active.

Zoning. Chambers that provide a relatively cool purge zone extend fromboth ends of the rectangular synthesis reactor. Applicants havedetermined that if a hot gas were to mix with the external environment(i.e., outside of the rectangular reactor), there would be increaseddegradation of the fiber material. The cool purge zones provide a bufferbetween the internal system and external environments. Carbon nanotubesynthesis reactor configurations known in the art typically require thatthe substrate is carefully (and slowly) cooled. The cool purge zone atthe exit of the present rectangular carbon nanotube growth reactorachieves the cooling in a short period of time, as required forcontinuous in-line processing.

Non-contact, hot-walled, metallic reactor. In some embodiments, ametallic hot-walled reactor (e.g., stainless steel) is employed. Use ofthis type of reactor can appear counterintuitive because metal, andstainless steel in particular, is more susceptible to carbon deposition(i.e., soot and by-product formation). Thus, most carbon nanotubesynthesis reactors are made from quartz because there is less carbondeposited, quartz is easier to clean, and quartz facilitates sampleobservation. However, Applicants have observed that the increased sootand carbon deposition on stainless steel results in more consistent,efficient, faster, and stable carbon nanotube growth. Without beingbound by theory it has been indicated that, in conjunction withatmospheric operation, the CVD process occurring in the reactor isdiffusion limited. That is, the carbon nanotube-forming catalyst is“overfed;” too much carbon is available in the reactor system due to itsrelatively higher partial pressure (than if the reactor was operatingunder partial vacuum). As a consequence, in an open system—especially aclean one—too much carbon can adhere to the particles of carbonnanotube-forming catalyst, compromising their ability to synthesizecarbon nanotubes. In some embodiments, the rectangular reactor isintentionally run when the reactor is “dirty,” that is with sootdeposited on the metallic reactor walls. Once carbon deposits to amonolayer on the walls of the reactor, carbon will readily deposit overitself. Since some of the available carbon is “withdrawn” due to thismechanism, the remaining carbon feedstock, in the form of radicals,reacts with the carbon nanotube-forming catalyst at a rate that does notpoison the catalyst. Existing systems run “cleanly” which, if they wereopen for continuous processing, would produce a much lower yield ofcarbon nanotubes at reduced growth rates.

Although it is generally beneficial to perform carbon nanotube synthesis“dirty” as described above, certain portions of the apparatus (e.g., gasmanifolds and inlets) can nonetheless negatively impact the carbonnanotube growth process when soot creates blockages. In order to combatthis problem, such areas of the carbon nanotube growth reaction chambercan be protected with soot inhibiting coatings such as, for example,silica, alumina, or MgO. In practice, these portions of the apparatuscan be dip-coated in these soot inhibiting coatings. Metals such asINVAR® can be used with these coatings as INVAR has a similar CTE(coefficient of thermal expansion) ensuring proper adhesion of thecoating at higher temperatures, preventing the soot from significantlybuilding up in critical zones.

Combined Catalyst Reduction and Carbon Nanotube Synthesis. In the carbonnanotube synthesis reactor disclosed herein, both catalyst reduction andcarbon nanotube growth occur within the reactor. This is significantbecause the reduction step cannot be accomplished timely enough for usein a continuous process if performed as a discrete operation. In atypical process known in the art, a reduction step typically takes 1-12hours to perform. Both operations occur in a reactor in accordance withthe present disclosure due, at least in part, to the fact thatcarbon-containing feedstock gas is introduced at the center of thereactor, not the end as would be typical in the art using cylindricalreactors. The reduction process occurs as the fiber material enters theheated zone. By this point, the gas has had time to react with the wallsand cool off prior to reducing the catalyst (via hydrogen radicalinteractions). It is this transition region where the reduction occurs.At the hottest isothermal zone in the system, carbon nanotube growthoccurs, with the greatest growth rate occurring proximal to the gasinlets near the center of the reactor.

In some embodiments, when loosely affiliated fiber materials including,for example, tows or rovings are employed (e.g., a glass roving), thecontinuous process can include steps that spread out the strands and/orfilaments of the tow or roving. Thus, as a tow or roving is unspooled itcan be spread using a vacuum-based fiber spreading system, for example.When employing sized glass fiber rovings, for example, which can berelatively stiff, additional heating can be employed in order to“soften” the roving to facilitate fiber spreading. The spread fiberswhich contain individual filaments can be spread apart sufficiently toexpose an entire surface area of the filaments, thus allowing the rovingto more efficiently react in subsequent process steps. For example, aspread tow or roving can pass through a surface treatment step that iscomposed of a plasma system as described above. The roughened, spreadfibers then can pass through a carbon nanotube-forming catalyst dipbath. The result is fibers of the glass roving that have catalystparticles distributed radially on their surface. The catalyzed-ladenfibers of the roving then enter an appropriate carbon nanotube growthchamber, such as the rectangular chamber described above, where a flowthrough atmospheric pressure CVD or plasma enhanced-CVD process is usedto synthesize carbon nanotubes at rates as high as several microns persecond. The fibers of the roving, now having radially aligned carbonnanotubes, exit the carbon nanotube growth reactor.

Although the invention has been described with reference to thedisclosed embodiments, one of ordinary skill in the art will readilyappreciate that these only illustrative of the invention. It should beunderstood that various modifications can be made without departing fromthe spirit of the invention.

1. A electrical device comprising: a first electrode layer; and a secondelectrode layer; wherein the first electrode layer and the secondelectrode layer comprise a plurality of continuous fibers that areinfused with carbon nanotubes.
 2. The electrical device of claim 1,further comprising: a base plate; a layer of separator material disposedbetween the first electrode layer and the second electrode layer;wherein the separator material is permeable to ions of an electrolyte;and an electrolyte in contact with the first electrode layer and thesecond electrode layer.
 3. The electrical device of claim 2, wherein theplurality of continuous fibers of the first electrode layer areconformally wound about the base plate and the plurality of continuousfibers of the second electrode layer are conformally wound about thelayer of separator material.
 4. The electrical device of claim 3,wherein there is substantially no overlap of the plurality of continuousfibers in adjacent windings about the base plate and the layer ofseparator material.
 5. The electrical device of claim 3, furthercomprising: at least one additional layer of separator material; and atleast one additional electrode layer comprising a plurality ofcontinuous fibers that are infused with carbon nanotubes; wherein eachelectrode layer is separated from one another by a layer of separatormaterial; and wherein the electrolyte is in contact with each electrodelayer.
 6. The electrical device of claim 5, further comprising: an outerinsulator casing.
 7. The electrical device of claim 2, wherein the baseplate, the first electrode layer, the second electrode layer, and thelayer of separator material reside in a reservoir of the electrolyte. 8.The electrical device of claim 2, further comprising: a first electrodeterminal connected to the plurality of continuous fibers of the firstelectrode layer; and a second electrode terminal connected to theplurality of continuous fibers of the second electrode layer.
 9. Theelectrical device of claim 8, wherein the first electrode terminal andthe second electrode terminal are located on the base plate.
 10. Theelectrical device of claim 1, wherein the plurality of continuous fiberscomprise a fiber form selected from the group consisting of a fiber tow,a fiber tape, a fiber ribbon, and combinations thereof.
 11. Theelectrical device of claim 1, wherein the plurality of continuous fibersare substantially parallel to one another in the first electrode layerand the second electrode layer.
 12. The electrical device of claim 1,wherein the continuous fibers are electrically conductive before beinginfused with carbon nanotubes.
 13. The electrical device of claim 12,wherein the continuous fibers comprise continuous metal fibers.
 14. Theelectrical device of claim 12, wherein the continuous fibers comprisecontinuous carbon fibers.
 15. The electrical device of claim 1, whereinthe continuous fibers are electrically non-conductive before beinginfused with carbon nanotubes.
 16. The electrical device of claim 15,further comprising: a conductivity enhancer associated with the firstelectrode layer and the second electrode layer; wherein the conductivityenhancer comprises a metal form selected from the group consisting ofmetal foils, metal ribbons, metal powders, metal nanoparticles, andcombinations thereof.
 17. The electrical device of claim 1, furthercomprising: an outer insulator casing.
 18. The electrical device ofclaim 17, wherein the outer insulator casing comprises a shrink wrapmaterial.
 19. The electrical device of claim 1, wherein the electricaldevice comprises a supercapacitor.
 20. The electrical device of claim19, wherein the supercapacitor has a capacitance of at least about 1Farad/gram of continuous fibers.
 21. The electrical device of claim 20,wherein the supercapacitor has a capacitance of at least about 2Farad/gram of continuous fibers.
 22. The electrical device of claim 1,wherein the infused carbon nanotubes are substantially perpendicular tothe surface of the continuous fibers.
 23. The electrical device of claim1, wherein the electrolyte comprises an inorganic electrolyte.
 24. Theelectrical device of claim 1, wherein the electrolyte comprises anorganic electrolyte.
 25. A method comprising: providing a plurality ofcontinuous fibers that are infused with carbon nanotubes; forming afirst electrode layer from a first portion of the plurality ofcontinuous fibers; and forming a second electrode layer from a secondportion of the plurality of continuous fibers.
 26. The method of claim25, further comprising: applying a layer of separator material betweenthe first electrode layer and the second electrode layer; wherein theseparator material is permeable to ions of an electrolyte; and exposingthe first electrode layer and the second electrode layer to anelectrolyte.
 27. The method of claim 26, wherein forming a firstelectrode layer comprises winding the first portion of the plurality ofcontinuous fibers conformally about a base plate; and wherein forming asecond electrode layer comprises winding the second portion of theplurality of continuous fibers conformally over the first electrodelayer.
 28. The method of claim 27, wherein winding the first portion ofthe plurality of continuous fibers conformally about a base plate,winding the second portion of the plurality of continuous fibersconformally over the first electrode layer, and applying a layer ofseparator material between the first electrode layer and the secondelectrode layer all occur simultaneously.
 29. The method of claim 27,wherein there is substantially no overlap of the plurality of continuousfibers in adjacent windings of the first electrode layer and the secondelectrode layer.
 30. The method of claim 26, wherein the first electrodelayer is exposed to the electrolyte before applying the layer ofseparator material.
 31. The method of claim 26, wherein the firstelectrode layer and the second electrode layer are simultaneouslyexposed to the electrolyte.
 32. The method of claim 31, wherein thefirst electrode layer and the second electrode layer are simultaneouslyimmersed in a reservoir of the electrolyte.
 33. The method of claim 26,further comprising: applying at least one additional layer of separatormaterial over the second electrode layer; and winding at least oneadditional electrode layer over the second electrode layer; wherein theat least one additional electrode layer comprises a plurality ofcontinuous fibers that are infused with carbon nanotubes; wherein eachelectrode layer is separated from one another by a layer of separatormaterial; and wherein the electrolyte is in contact with each electrodelayer.
 34. The method of claim 33, further comprising: applying an outerinsulator casing.
 35. The method of claim 25, wherein the plurality ofcontinuous fibers comprise a fiber form selected from the groupconsisting of a fiber tow, a fiber tape, a fiber ribbon, andcombinations thereof.
 36. The method of claim 25, wherein the pluralityof continuous fibers are substantially parallel to one another in thefirst electrode layer and the second electrode layer.
 37. The method ofclaim 25, further comprising: applying an outer insulator casing. 38.The method of claim 25, wherein the continuous fibers are conductivebefore being infused with carbon nanotubes; wherein the continuousfibers are selected from the group consisting of continuous metalfibers, continuous carbon fibers, and combinations thereof.
 39. A methodcomprising: providing a plurality of continuous fibers that are infusedwith carbon nanotubes; forming a first electrode layer by winding aportion of the plurality of continuous fibers conformally about a baseplate; and forming at least two additional electrode layers over thefirst electrode layer by winding separate portions of the plurality ofcontinuous fibers conformally over the first electrode layer.
 40. Themethod of claim 39, further comprising: applying a layer of separatormaterial between each electrode layer; wherein the separator material ispermeable to ions of the electrolyte; and exposing the first electrodelayer and the at least two additional electrode layers to anelectrolyte.
 41. The method of claim 40, wherein the first electrodelayer is exposed to the electrolyte before applying a layer of separatormaterial.
 42. The method of claim 40, wherein the first electrode layerand the at least two additional electrode layers are simultaneouslyexposed to the electrolyte.
 43. The method of claim 39, wherein thecontinuous fibers are conductive before being infused with carbonnanotubes; wherein the continuous fibers are selected from the groupconsisting of continuous metal fibers, continuous carbon fibers, andcombinations thereof.
 44. The method of claim 39, wherein the pluralityof continuous fibers comprise a fiber form selected from the groupconsisting of a fiber tow, a fiber tape, a fiber ribbon, andcombinations thereof.